Dynamoelectric machine commutator



Aug. 5, 1952 A. H. LABASTlE DYNAMOELECTRIC MACHINE COMMUTATOR Filed March 16, 1951 Ill! Inventor: Albert H..Labastie,

' His Attorne gc Patented Aug. 5, 1952 UNITED STATE DYNAMOELECTRIC MACHINE COMMUTATOR Albert H.

to General Electric Company,

New York Labastie, West Medford, Mass., assignor a corporation of Application March 16, 1951, Serial No. 215,964

4 Claims. 1

My invention relates to dynamoelectric machine commutators and has particular significanoe in connection with commutators of the shrink ring type.

It has long been known to construct a commutator by providing a central shell (for securing the commutator to a shaft), placing the individual copper commutator segments around the periphery of the shell, and then binding the individual segments in place by one or more metallic "shrink rings, so called because such a ring is first heated and then shrunk in place around an end of the segments to hold the latter securely against centrifugal and other forces. Inasmuch as the individual segments must act as individual electrical conductors, it is necessary that insulation be interposed both between segments and between each such ring and adjacent segment faces and between the shell and segment faces adjacent thereto. The insulation adjacent the ring inner peripheries and adjacent the shell outer periphery must stand up under the high stresses of shrinking during assembly and must also stand up under the operative stresses of centrifugal force and expansion differences during duty cycles of heating and cooling. In the past, there has not been found an insulation which is satisfactory for such an installation under all conditions. While mica has been used, it often exhibits a tendency to peel, shear, slip (internally), crack or powder thereby causing the commutator to become out of round to such an extent that it soon sparks and grinds itself (or associated brushes) to destruction.

It is an object of the present invention to provide simple and inexpensive means for overcoming the above mentioned difficulties.

Another object of the present invention is to provide a shrink ring type commutator assembly in which all substantially peripheral insulation provides a smooth surface of strong homogeneous material which, unlike mica, for example, will not peel or slip and which, unlike vitreous material such as glass, will not rupture or crack at points of pressure, but will under all ordinary conditions of operation permanently maintain both its insulating properties and mechanical stability.

Briefly stated, in accordance with one aspect of my invention, I eliminate the primary insulation problems present in conventional shrink ring type commutators by employing shrink rings which have molded, on their inner diameters, a relatively homogeneous insulation comprising, for example, finely ground particles of glass and mica, and by also employing a shaft engaging shell which has molded on the other periphery thereof the same or a like relatively homogeneous material. i

My invention will be better understood from consideration of the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. 7

The single figure of the drawing represents a sectional view of a shrink ring type commutator assembly adapted to be driven by a shaft III shown provided with a keyway H and key I2 for rotationally engaging a metallic shell or sleeve 13, preferably made of metal such as steel. In order to provide means for exerting outward pressure on the commutator assembly (addi tional and opposite to that of the inward pressure provided by the shrink rings. as hereinafter explained) the outer diameter of the shell I3 is on a taper and, although this feature is not essential, the taper is shown terminating in a threaded portion H for receiving a nut [5. To provide a surface to which molded material will unslippingly adhere, the shell tapered surface is roughened, being, for example, notched in a grid pattern as shown at I6 and then (and before assembly) an insulation body 11 is molded under heat and pressed directly onto the sleeve 13 tapered and roughened surface to present a smooth and solid surface the accuracy of which is limited only by that of the mold that is used.

The insulation I1 is preferably an aggregate inorganic base molding compound, the aggregate being of finely divided natural silicate (for example, mica) with a bonding agent of finely divided vitreous material (for example, glass).

The commutator assembly includes a plurality of copper commutator segments l8 held in place by steel shrink rings I9. All radially extending surfaces (such as those between the segments themselves and those between the segment ends and the shrink rings and between the segments and the nut I5 or an associated metallic washer 20) may be of conventional natural or pasted mica 2| since these faces will not be subjected to high pressures. The commutator segment assembly may be driven over the taper of insulation I! in a press and it is contemplated that the taper shall be a holding taper which will not slip, th nut (or other fastening means) being merely an added precaution for positive holding.

The steel shrink rings l9 (before being shrunk on the segments) are first provided on their inner peripheries with a roughened or serrated surtion so that the finished assembly wil1 permanently retain the original accuracy of commutator alignment as well as all desired insulatin properties. While I have illustrated and described a particular embodiment of my invention, modifications metallic central shell adapted to rotationally engage a dynamoelectrio machine shaft, said shell having a roughened outer periphery and premolded thereto a hard molded insulating body comprising an aggregate of finely divided mica and finely divided vitreous material, a plurality of metallic commutator segments arranged peripherally around said insulating-body, a plurality of metallic shrink rings for holding said segments in place, said shrink rings each having a roughened inner periphery and pre-molded thereto .ahard molded insulating body comprising an aggregate of finely divided mica and finely dividthereof will occur to those skilled in the art. .I

desire it to be understood, therefore, that my in vention is not to be limited to the particular-:at-

rangements described and I intend in the appended claims to cover al-Lmodifications which do not departfromthe spirit and-scope of my invention. What I claim as new and desirerto secure by Letters Patent of the United States is: 9 1, A dynamoelectricmachine shrink, ring type commutator comprisingta a u ar-i r shell provided with aroughcned outer periphery. having alayer ofinsulationpre-molded thereto, a plurality of interinsulated commutator segments surrounding said insulation pre-moldedi on said shell, and a plurality of shrink rings eachhaving a roughened inner periphery and a, layer of -insulation pre-molded thereto, said rings being shrunk around portions of said segments to hold the latter tightly on said'shell While said premolded insulation "provided ons'hell'and rings maintains mechanical alignment and desired insulating properties. i.

2. In a dynamoelectric machine-shrink ring type commutator, the combination of at least one shrink ring having. a roughened inner peripheral surface'and pre-moldedthereto a hard molded insulatin body comprising an aggregate inorganic base molding compound of finely divided material silicate with a-bonding agent of finely divided vitreous material, 1 v V V 3.'In a shrink ring type commutator for a dynamoelectric machine; the combination of a ed vitreous material interposed between the respective ring and said commutator segments,

whereby the "primarily peripherally extending mating inner surfaces of the metallic members of said shrink ring type commutator will have interposed therebetween a uniform hard insulation such that the finished assembly may permanently retain its original accuracy and insulating properties. I

4. The combination as in claimi'urther characterized by said shell outer periphery b'eing provided on a taper for placing radial pressure on saidsegments opposite to that provided by said shrink rings, said taper'terrninating at its smaller diameter end in a fastening means receiving portion, and fastening means cooperating with said portion to provide positive holding of said commutator segments on said insulated tapered shell.

- ALBERT H. LABASTIE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Germany Jan. 9, 1911 

